As an increasing number of electronic appliances such as video or audio apparatuses or PCs have been used in a home and digital techniques have become dominant in video and audio signal processing, the need for communication between home electronic appliances or communication with other networks is also increasing. In addition, the demand for controlling home electronic appliances through a single mobile apparatus such as a PDA is also increasing.
To meet the demand, home networking technology has emerged for connecting home electronic appliances such as digital TVs or DVD players. The UPnP (Universal Plug and Play) is a key technology required for implementing the home network.
FIG. 1 shows an exemplary UPnP network. According to the UPnP specification, every home network requires an apparatus called the IGD (Internet Gateway Device) 20, which assigns addresses to elements or nodes 10, 11, 12 connected to the network and also acts as a gateway to external networks, e.g., the Internet. The IGD 20 can be a stand-alone device or embedded within another apparatus such as a PC or refrigerator.
Each UPnP network has a control point (CP) 10, which discovers and controls devices connected to the UPnP network, processes events, and enables query and control through the provided user interface (UI). Precisely speaking, the control point is a control application program executed on a device. However, the device executing the control application program is also referred to as the control point.
The control point 10 provides the UPnP discovery service at startup, which finds electronic devices connected to the home network by transmitting a search message to the home network and obtains information regarding the found devices. The control point 10 then provides the obtained information for a user through a user interface specially designed for the home network, thereby allowing the user to request a certain service using the user interface.
The user of the home network may want to request remote query or control for a device on the home network from outside the home network. In this case, however, the user cannot access the home network through the Internet simply by using the control point 10 at a remote location. Even in the case where the user utilizes a proper remote access application program (e.g., virtual private network (VPN) application), communication errors are likely to occur due to a failure in the communication protocol caused by a time delay in the communication between the home network and the remote site.